4 Dr. P. H. Carpenter on the 



central plate of the Echinoderm apical system has been 

 repeatedly noticed by us botli and also by others under the 

 name " dorsocentral ; " and zoologists have been warned 

 again and again not to confuse it with the enlarged top stem- 

 joint in the stem of many Crinoids, for which, in the case of 

 Comatula^ Miiller and his successors had employed the name 

 " ceutro-dorsal." Early in 1887 Duncan and Sladen *, 

 writing on the morphology of the Saleniidge, frequently re- 

 ferred to the so-called sur-anal plate of Echinids as the dorso- 

 central, mentioning at the same time its homologies in the 

 Asterids and Ophiurids. Fcwkes f, who had previously 

 confounded dorsocentral and centro-dorsal, wrote a short time 

 later in the same terms. But all our efforts to obtain a greater 

 precision of nomenclature seem to have been in vain, for even 

 such a well-informed writer as the late Professor Neuma}^- X 

 alluded in 1888 to " die centrodorsale Platte bei Salenien." 

 Unaware, too, that the presence of independent under-basals in 

 the Antedo7i-\ixr\^ had been announced by Bury § in 1887, he 

 concluded that they are represented by the " ccntrale Platte," 

 by which he meant the eidarged top stem-joint or centro- 

 dorsal. But as he also recognized the fact that these under- 

 basals are well developed in Marsupites and enclose " eine 

 grosse centrodorsale Tafel," he was driven to the following 

 conclusions || : — " Es scheint demnach, als ob die centro- 

 dorsale Platte der ausgewachsenen Crinoiden durchaus nicht 

 immcr dicselbc morpliologischc Bedcutung luitte, und audi 

 durchaus nicht nothwendig immer dem o-leichnamiijcn Theile 

 der Antedon-ljViXWQ, cntsprachc." But is it so certain that the 

 central plate in the calyx of Marsupites should be called a 

 centro-dorsal at all, i. e. that it is an enlarged top stem-joint ? 

 Twelve years ago I gave reasons for believing it to be a 

 primitively imperforate plate homologous Avith the dorso- 

 central of SaJenia, and not a top stem-joint with its central 

 canal obscured by a secondary calcareous deposit^. ^ly 

 arguments have never been refuted ; but paleontologists have 

 nevertheless continued to speak of the centro-dorsal of Mar- 



• " On some Points in the Morpholngy and Classification of the 

 Saleniidse, Agassiz," Ann. & Mag. Nat. Hist.' 1887, ser. 5, vol. xix. pp. llf), 

 121. 



t Bull. Mus. Comp. Zoiil. 1888, vol. xvii. p. 38. 



\ ' Die Stiimme des Thierreichs,' Wieii, 1880, l^d. i. p. 403. 



§ " The Early Stages in the Development of Aiitedon rosacea," Report 

 of the Fifty-seventh Meeting of the Briti.<h Association, held at Mim- 

 chester, 188? : London, 1888, p. 735. Also Proc. Roy. Soc. 1887-68, 

 vol. xliii. p. 200. 



I| Op. cit. p. 403. 



^ Quart. .lourn. Micr. Soi. 1S7.'^, vol. xviii. pp. 3S0, ;$.<!. 



